Question

Factorise using the grouping method :
a² + 4b² - 3a + 6b - 4ab

Answer 1

a² + 4b² - 3a + 6b - 4ab
= a² + 4b² - 4ab - 3a + 6b
= a² + (2b)² - 2 × a × (2b) - 3(a - 2b)    [As (a - b)² = a² - 2ab + b² ]
= (a - 2b)² - 3(a - 2b)
= (a - 2b)[(a - 2b)- 3]
= (a - 2b)(a - 2b - 3)